1. Field of the Invention
The present invention relates to a solar generator system including a solar cell for photo-electrically converting sunlight, a lens for condensing and converging the sunlight to the solar cell, and a secondary light-condenser which is formed into an inversed truncated conical shape with a portion adjacent to the lens being of a larger diameter, and which is disposed on the solar cell with a light-receiving surface being opposed to the lens so as to introduce converged rays from the lens to the solar cell.
2. Description of the Related Art
Such a solar generator system is already known, for example, from Japanese Patent Application Laid-open No.7-231111.
When the focus of a lens is set on a solar cell to condense the sunrays onto the solar cell by the lens to generate an electric power, the sunrays are too concentrated locally. For this reason, there is a possibility that a disturbance may be produced in flows of electrons produced in the solar cell by the photoelectric conversion and as a result, the generating efficiency is reduced, and the solar cell is raised locally in temperature to a high level and thermally deteriorated. In addition, the light-condensing efficiency is degraded largely even by a slight displacement of the light-condensing position. Therefore, particularly, when a system for generating an electric power by tracking sunrays is constructed, the light-condensing efficiency may be reduced largely due to an influence of a mechanical error in a tracking device or the like.
On the contrast, in the system disclosed in the above Japanese Patent Application Laid-open No.7-231111, a secondary light-condenser of a single-cone type is placed on a solar cell and formed with a side of an inversed truncated conical optical lens body having a planar light-receiving surface being covered with a metal or the like. The light-condensing efficiency can be enhanced by the secondary light-condenser, and even if a slight displacement of an angle of irradiation of sunlight to the lens is produced, a reduction in performance can be compensated for by covering the slight displacement by the relatively wide light-receiving surface of the secondary light-condenser. The effective condensing of the sunlight is possible, but is insufficient for the purpose of avoiding the local concentration of the sunlight in order to prevent a reduction in power-generating efficiency and a thermal deterioration. When the light-condensing magnification is increased, any measure is required.
On the other hand, as disclosed in Japanese Patent Application Laid-open No.7-92309, it is a conventional practice to increase the width of an effective light flux applied to a solar cell by use of a multi-focus linear Fresnel lens, so that even if the angle of irradiation of sunlight to the lens is displaced slightly, the local convergence of the sunlight to the solar cell can be avoided, while avoiding a remarkable reduction in light-condensing efficiency. However, a portion of the light condensed by the lens is wasted and for this reason, a reduction in power-generating efficiency is unavoidable.
Accordingly, it is an object of the present invention to provide a solar generator system, wherein even if the sunlight to the lens is displaced slightly, the light-condensing efficiency can be prevented from being degraded largely, and the occurrences of a reduction in power-generating efficiency and a thermal deterioration can be prevented.
To achieve the above object, according to a first aspect and feature of the present invention, there is provided a solar generator system comprising a solar cell for photo-electrically converting sunlight, a lens for condensing and converging the sunlight to the solar cell, and a secondary light-condenser which is formed into an inversed truncated conical shape with a portion adjacent to the lens being of a larger diameter, the secondary light-condenser being disposed on the solar cell with a light-receiving surface being opposed to the lens so as to introduce converged rays from the lens to the solar cell, wherein the light-receiving surface of the secondary light-condenser is formed into a truncated conical shape and has a circular planar portion, and a slant portion which is formed into a tapered shape with the diameter thereof being larger as the slant portion goes away from the lens and which has a smaller-diameter end connected to an outer periphery of the planar portion, and the lens comprises a multi-focus lens with foci set on the side of the light-receiving surface being displaced from one another.
With such arrangement, the inverted truncated conical secondary light-condenser is placed on the solar cell and hence, even if a slight displacement of an angle of irradiation of the sunlight to the lens is produced, this displacement can be corrected by the secondary light-condenser to prevent a large degradation in light-condensing efficiency. In addition, since the lens is the multi-focus lens, the sunrays condensed by the lens are dispersed and irradiated to the secondary light-condenser, and the rays from the lens are refracted in different directions by the secondary light-condenser of a cornet type and introduced to the solar cell. Therefore, it is possible to avoid that the sunrays are locally concentrated and converged onto the surface of the solar cell, thereby preventing the temperature of the solar cell from locally rising to reduce the generating efficiency and to produce a thermal deterioration. To further disperse the rays from the lens to introduce them to the solar cell, a secondary light-condenser of a top-dome type with a light-receiving face formed into a spherical crown-shape can be used. However, when the top-dome type secondary light-condenser is used, a light flux in a central area may be reduced remarkably due to the displacement of a light-condensing position in some cases and hence, there is a possibility that an outer peripheral portion of the solar cell is raised in temperature to a high level and thermally deteriorated. On the contrast, in a cornet-type secondary light-condenser, the light flux can be dispersed in an entirely well-balanced manner, as compared with the top-dome type secondary light-condenser and hence, there is not a possibility that a thermal deterioration of the above-described type is produced. Moreover, the cornet-type secondary light-condenser is also easy to manufacture, as compared with the top-dome type secondary light-condenser.
According to a second aspect and feature of the present invention, in addition to the first feature, the lens is a circular Fresnel lens having an outer surface formed into a polygonal shape. With such configuration, when a generating unit is constructed using large numbers of lenses, secondary light-condensers and solar cells in combination, a space required for the disposition of the large number of lenses can be reduced in size, as compared with circular lenses, whereby the generating unit can be formed compactly.
According to a third aspect and feature of the present invention, in addition to the first or second feature, the inclination angle of the slant portion is set at a value ensuring the avoidance of the total reflection of light irradiated from the lens to the slant portion. With such feature, it is possible to introduce rays condensed by the lens to the solar cell with being wasted, thereby further enhancing the generating efficiency.
According to a fourth aspect and feature of the present invention, in addition to the first or second feature, the lens is formed such that the focus of an outermost lens portion of the lens is located at a point closer to the center of the planar portion. With such feature, even if a slight displacement of the light-condensing position is produced due to the retardation of the tracking of sunlight, an assembling error or the like, rays from the lens can be irradiated or applied reliably to the secondary light-condenser, thereby effectively inhibiting the degradation in a light-condensing efficiency.
According to a fifth aspect and feature of the present invention, in addition to the first or second feature, the planar portion is disposed at a location displaced from a focus position of the entire lens in a direction away from the lens. With such feature, rays from the lens can be faded as a whole and irradiated or applied to the secondary light-condenser, and the rays applied from the lens to the secondary light-condenser can be faded by the displacement of the light-condensing position. Thus, even if a slight displacement of a light-condensing position is produced due to the retardation of the tracking of sunlight, an assembling error or the like, rays from the lens can be irradiated reliably to the secondary light-condenser, thereby effectively inhibiting the degradation of the light-condensing efficiency.
The above and other objects, features and advantages of the invention will become apparent from the following description of the preferred embodiment taken in conjunction with the accompanying drawings.